The preparation of mono-long chain amine oxide surfactants by the oxidation of tertiary amines is of considerable commercial interest. Such surfactants are widely used in commercial cleaning compositions, especially high sudsing dishwashing detergents. Such concentrated solutions are especially useful in formulating concentrated or "compact" liquid detergent compositions which are now favored by many consumers and generally contain lower amounts of water than conventional detergents. However, the formulation of mono-long chain amine oxide surfactants containing high levels, i.e., greater than about 30%, by weight of the amine, has proven to be a difficult problem to overcome. Typically, mono-long chain amine oxide surfactants containing above 30% active result in an unhandleable gel especially when a phase modifying solvent is not incorporated. Also, some sources of mono-long chain amine oxide surfactants may be contaminated with residual amounts of nitrite materials, especially inorganic nitrites. Contamination by such nitrites may be tolerable under many circumstances. For some uses however, the presence of nitrites may be undesirable, since they can react with other ingredients which may be present in the fully formulated detergent compositions.
U.S. Pat. No. 5,583,258, issued Dec. 10, 1996 to Hawkins describes an economical process for preparing concentrated (greater than 30%) free flowing aqueous amine oxide solutions having reduced levels of nitrites and nitrosamines, and achieving said free flowing properties without the use of phase-modifying solvents. In that process, tertiary amine and hydrogen peroxide are reacted in the presence of up to 2.5% alkali metal bicarbonate (based on weight of the amine). The reaction temperature is in the range of 40-100.degree. C. and the ratio of hydrogen peroxide to amine is 95%-125% of stoichiometric. The Hawkins reference is silent with respect to residual levels of hydrogen peroxide.
It has now been found that the presence of even relatively small amounts of hydrogen peroxide (i.e. in excess of 50 ppm or so) in amine oxides used in formulation of liquid detergents can result in odor problems, especially if the liquid detergents contain diamine compounds such as diaminopentane, which is a very effective buffer for use in such compositions. Also, when used in formulation of liquid detergents containing enzymes to enhance cleaning, amine oxides containing such relatively small amounts of hydrogen peroxide can cause degradation of the enzymes.
It is an objective of the present invention to produce high active aqueous amine oxides having residual hydrogen peroxide levels of less than 50 ppm, as well as having suppressed levels of nitrites and nitrosamines, and having free flowing properties without the use of phase modifying solvents.
It is another objective of the invention to produce said amine oxides at minimal reaction time.
All documents referred to herein are incorporated by reference and all percentages and ratios are "by weight" unless specified otherwise.